diff --git a/pom.xml b/pom.xml
index 8fa4433..115f598 100644
--- a/pom.xml
+++ b/pom.xml
@@ -76,6 +76,14 @@
     </dependency>
     <!-- https://mvnrepository.com/artifact/org.json/json -->
 
+    <!-- mapDB kv存储 -->
+    <!-- https://mvnrepository.com/artifact/org.mapdb/mapdb -->
+    <dependency>
+        <groupId>org.mapdb</groupId>
+        <artifactId>mapdb</artifactId>
+        <version>3.0.8</version>
+    </dependency>
+
 </dependencies>
 
 </project>
\ No newline at end of file
diff --git a/src/main/java/minsecurity/identity/Identity.java b/src/main/java/minsecurity/identity/Identity.java
index b16efd0..f678dd4 100644
--- a/src/main/java/minsecurity/identity/Identity.java
+++ b/src/main/java/minsecurity/identity/Identity.java
@@ -20,6 +20,7 @@ import javax.crypto.BadPaddingException;
 import javax.crypto.IllegalBlockSizeException;
 import javax.crypto.NoSuchPaddingException;
 import java.io.IOException;
+import java.io.Serializable;
 import java.security.InvalidAlgorithmParameterException;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
@@ -43,10 +44,12 @@ public class Identity {
     private PublicKeyInterface Pubkey;
     private String Passwd;
     private Certificate Cert;
+    private boolean IsDefault;
 
     public Identity(String name, KeyParam keyParam,
                     PrivateKeyInterface prikey, byte[] prikeyRawByte,
-                    PublicKeyInterface pubkey, String passwd, Certificate cert) {
+                    PublicKeyInterface pubkey, String passwd, Certificate cert,
+                    boolean isDefault) {
         Name = name;
         KeyParam = keyParam;
         Prikey = prikey;
@@ -54,6 +57,7 @@ public class Identity {
         Pubkey = pubkey;
         Passwd = passwd;
         Cert = cert;
+        IsDefault = isDefault;
     }
 
 
@@ -240,16 +244,27 @@ public class Identity {
         Cert = cert;
     }
 
+    public boolean isDefault() {
+        return IsDefault;
+    }
+
+    public void setDefault(boolean aDefault) {
+        IsDefault = aDefault;
+    }
+
     @Override
     public String toString() {
         return "Identity{" +
                 "Name='" + Name + '\'' +
-                ", KeyParam=" + KeyParam +
-                ", Prikey=" + Prikey +
+                ", KeyParam.signAlgo=" + KeyParam.SignatureAlgorithm +
+                ", KeyParam.pubAlgo=" + KeyParam.PublicKeyAlgorithm +
+                ", Prikey=" + ByteUtils.toHexString(Prikey.getBytes()) +
+                ", pubKey=" + ByteUtils.toHexString(Pubkey.getBytes()) +
                 ", PrikeyRawByte=" + (PrikeyRawByte == null ? "null":ByteUtils.toHexString(PrikeyRawByte)) +
                 ", Pubkey=" + Pubkey +
                 ", Passwd='" + Passwd + '\'' +
                 ", Cert=" + Cert +
+                ", isDefault=" + IsDefault +
                 '}';
     }
 }
diff --git a/src/main/java/minsecurity/identity/persist/IdentitySerializer.java b/src/main/java/minsecurity/identity/persist/IdentitySerializer.java
new file mode 100644
index 0000000..fea81d4
--- /dev/null
+++ b/src/main/java/minsecurity/identity/persist/IdentitySerializer.java
@@ -0,0 +1,97 @@
+package minsecurity.identity.persist;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import minsecurity.Common;
+import minsecurity.certificate.cert.CertException;
+import minsecurity.certificate.cert.CertUtils;
+import minsecurity.certificate.cert.Certificate;
+import minsecurity.crypto.sm2.SM2PrivateKey;
+import minsecurity.crypto.sm2.SM2PublicKey;
+import minsecurity.identity.Identity;
+import minsecurity.identity.KeyParam;
+import org.bouncycastle.pqc.math.linearalgebra.ByteUtils;
+import org.jetbrains.annotations.NotNull;
+import org.mapdb.DataInput2;
+import org.mapdb.DataOutput2;
+import org.mapdb.Serializer;
+
+import javax.crypto.BadPaddingException;
+import javax.crypto.IllegalBlockSizeException;
+import javax.crypto.NoSuchPaddingException;
+import java.io.IOException;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+import java.security.NoSuchProviderException;
+
+/*
+ * @Author: hongyu guo
+ * @Description: mapDB需要自定义序列化、反序列化方法
+ * @Version: 1.0.0
+ * @Date: 20:50 2021/03/09
+ * @Copyright: MIN-Group；国家重大科技基础设施——未来网络北大实验室；深圳市信息论与未来网络重点实验室
+ */
+public class IdentitySerializer implements Serializer<Identity> {
+
+
+    @Override
+    public void serialize(@NotNull DataOutput2 dataOutput2, @NotNull Identity identity) throws IOException {
+        String name = identity.getName();
+        String pub = ByteUtils.toHexString(identity.getPubkey().getBytes());
+        String priv = ByteUtils.toHexString(identity.getPrikey().getBytes());
+        int pubAlgo = identity.getKeyParam().PublicKeyAlgorithm;
+        int signAlgo = identity.getKeyParam().SignatureAlgorithm;
+        String passwd = identity.getPasswd();
+        String cert = "";
+        try {
+            cert = CertUtils.toPem(identity.getCert(),null, Common.SM4CBC);
+        } catch (CertException | NoSuchPaddingException | InvalidAlgorithmParameterException |
+                NoSuchAlgorithmException | IllegalBlockSizeException | BadPaddingException |
+                NoSuchProviderException | InvalidKeyException e) {
+            e.printStackTrace();
+        }
+        boolean isDefault = identity.isDefault();
+        String prikeyRawByte = identity.getPrikeyRawByte()== null ?
+                "" :ByteUtils.toHexString(identity.getPrikeyRawByte());
+
+
+        dataOutput2.writeUTF(name);
+        dataOutput2.writeUTF(pub);
+        dataOutput2.writeUTF(priv);
+        dataOutput2.writeInt(pubAlgo);
+        dataOutput2.writeInt(signAlgo);
+        dataOutput2.writeUTF(passwd);
+        dataOutput2.writeUTF(cert);
+        dataOutput2.writeBoolean(isDefault);
+        dataOutput2.writeUTF(prikeyRawByte);
+    }
+
+    @Override
+    public Identity deserialize(@NotNull DataInput2 dataInput2, int i) throws IOException {
+        String name = dataInput2.readUTF();
+        byte[] pub = ByteUtils.fromHexString(dataInput2.readUTF());
+        byte[] priv = ByteUtils.fromHexString(dataInput2.readUTF());
+        int pubAlgo = dataInput2.readInt();
+        int signAlgo = dataInput2.readInt();
+        String passwd = dataInput2.readUTF();
+        String certString = dataInput2.readUTF();
+        Certificate certificate = null;
+        try {
+            certificate = CertUtils.fromPem(certString, null, Common.SM4CBC);
+        } catch (CertException | BadPaddingException | NoSuchPaddingException |
+                InvalidAlgorithmParameterException | NoSuchAlgorithmException |
+                IllegalBlockSizeException | NoSuchProviderException | InvalidKeyException e) {
+            e.printStackTrace();
+        }
+        boolean isDefault = dataInput2.readBoolean();
+        byte[] prikeyRawByte = dataInput2.readUTF().equals("") ?
+                null : ByteUtils.fromHexString(dataInput2.readUTF());
+        KeyParam keyParam = new KeyParam(pubAlgo, signAlgo);
+        SM2PrivateKey sm2PrivateKey = new SM2PrivateKey();
+        sm2PrivateKey.setBytes(priv);
+        SM2PublicKey sm2PublicKey = new SM2PublicKey();
+        sm2PublicKey.setBytes(pub);
+        return new Identity(name,keyParam, sm2PrivateKey,prikeyRawByte, sm2PublicKey, passwd, certificate, isDefault);
+    }
+
+}
diff --git a/src/test/java/minsecurity/identity/TestIdentity.java b/src/test/java/minsecurity/identity/TestIdentity.java
index d8df6ae..45394bc 100644
--- a/src/test/java/minsecurity/identity/TestIdentity.java
+++ b/src/test/java/minsecurity/identity/TestIdentity.java
@@ -41,7 +41,7 @@ public class TestIdentity {
         SM2PrivateKey sm2PrivateKey = new SM2PrivateKey(d);
         SM2PublicKey sm2PublicKey = new SM2PublicKey(x,y);
         KeyParam keyParam = new KeyParam(Common.SM2, Common.SM3withSM2);
-        Identity identity = new Identity("root",keyParam,sm2PrivateKey,null,sm2PublicKey, "123456", null);
+        Identity identity = new Identity("root",keyParam,sm2PrivateKey,null,sm2PublicKey, "123456", null, false);
         Certificate certificate = new Certificate(1, 1, sm2PublicKey, null,
                 Common.SM3withSM2, Common.SM2, "root", "root",
                 System.currentTimeMillis() - 1000, System.currentTimeMillis() + 5000,
@@ -73,6 +73,8 @@ public class TestIdentity {
         idFromBytes = Identity.load(bytesOfDump, null);
         assertEquals(ByteUtils.toHexString(identity.getPrikey().getBytes()), ByteUtils.toHexString(idFromBytes.getPrikey().getBytes()));
         assertEquals(ByteUtils.toHexString(identity.getPubkey().getBytes()), ByteUtils.toHexString(idFromBytes.getPubkey().getBytes()));
+
+        logger.debug(identity.getPrikey().getBytes().length + " " + identity.getPubkey().getBytes().length);
     }
 
 
diff --git a/src/test/java/minsecurity/identity/TestPersist.java b/src/test/java/minsecurity/identity/TestPersist.java
new file mode 100644
index 0000000..8578ba6
--- /dev/null
+++ b/src/test/java/minsecurity/identity/TestPersist.java
@@ -0,0 +1,68 @@
+package minsecurity.identity;
+
+
+import minsecurity.Common;
+import minsecurity.certificate.cert.CertUtils;
+import minsecurity.certificate.cert.Certificate;
+import minsecurity.crypto.sm2.SM2Base;
+import minsecurity.crypto.sm2.SM2PrivateKey;
+import minsecurity.crypto.sm2.SM2PublicKey;
+import minsecurity.identity.persist.IdentitySerializer;
+import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
+import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
+import org.bouncycastle.crypto.params.ECPublicKeyParameters;
+import org.junit.Test;
+import org.mapdb.BTreeMap;
+import org.mapdb.DB;
+import org.mapdb.DBMaker;
+import org.mapdb.Serializer;
+import org.slf4j.LoggerFactory;
+
+import java.util.concurrent.ConcurrentMap;
+
+/*
+ * @Author: hongyu guo
+ * @Description:
+ * @Version: 1.0.0
+ * @Date: 17:35 2021/03/09
+ * @Copyright: MIN-Group；国家重大科技基础设施——未来网络北大实验室；深圳市信息论与未来网络重点实验室
+ */
+public class TestPersist {
+    private static final org.slf4j.Logger logger = LoggerFactory.getLogger(TestIdentity.class);
+
+    @Test
+    public void testMapDB() throws Exception {
+
+
+        AsymmetricCipherKeyPair keyPair = SM2Base.generateKeyPairParameter();
+        ECPrivateKeyParameters priKey = (ECPrivateKeyParameters) keyPair.getPrivate();
+        ECPublicKeyParameters pubKey = (ECPublicKeyParameters) keyPair.getPublic();
+        byte[] d = priKey.getD().toByteArray();
+        // d = Arrays.copyOf(d,32);
+        byte[] x = pubKey.getQ().getAffineXCoord().getEncoded();
+        byte[] y = pubKey.getQ().getAffineYCoord().getEncoded();
+        // BigInteger bigInteger = priKey.getD();
+        SM2PrivateKey sm2PrivateKey = new SM2PrivateKey(d);
+        SM2PublicKey sm2PublicKey = new SM2PublicKey(x,y);
+        KeyParam keyParam = new KeyParam(Common.SM2, Common.SM3withSM2);
+        Identity identity = new Identity("root",keyParam,sm2PrivateKey,null,sm2PublicKey, "123456", null, false);
+        Certificate certificate = new Certificate(1, 1, sm2PublicKey, null,
+                Common.SM3withSM2, Common.SM2, "root", "root",
+                System.currentTimeMillis() - 1000, System.currentTimeMillis() + 5000,
+                Common.CertSign, true, System.currentTimeMillis());
+        CertUtils.signCert(certificate, sm2PrivateKey);
+        identity.setCert(certificate);
+        DB db = DBMaker.fileDB("./target/test.db").closeOnJvmShutdown().transactionEnable().make();
+        Serializer<Identity> customSerializer = new IdentitySerializer();
+        ConcurrentMap<String, Identity> map =  db.hashMap("identity")
+                                        .keySerializer(Serializer.STRING)
+                                        .valueSerializer(customSerializer)
+                                        .createOrOpen();
+        // map.put("/min/test05", new Identity());
+        map.put("/min/test06", identity);
+        db.commit();
+        logger.debug(identity.toString());
+        Identity id = map.get("/min/test06");
+        logger.debug(id.toString());
+    }
+}